Today, most RF output filters for the cellular frequency band are manufactured either by machining cavities in large blocks of aluminum or by die casting large aluminum parts. Both methods produce heavy and expensive RF filters. Also, both methods further require the machining of a cover for the cavity filter, which is attached to the base of the machined aluminum part with a significant number of screws to guarantee an effective RF seal thereby increasing the cost and complexity of the process. It may also be required to plate a thin layer of silver onto the aluminum to enhance the filter performance.
Another limitation of the conventional methods is the restriction imposed by conventional machining techniques, which typically require the cavity to have vertical walls with a radius along the bottom and side corners and a square corner (which is undesirable) where the cover seals to the top of the cavity.